Electric system and indicating circuit therefor



Sept. 8, 1942. a. L. ROGERS 2,295,293

ELECTRIC SYSTEM AND INDICATING CIRCUIT THEREFOR Original Filed July 31, 1941 3 She ets-Sheet 1 Inventor George L. Roger's,

His Attorney.

P 1942- s. L. ROGERS 2,295,293

ELECTRIC SYSTEM AND INDICATING CIRCUIT THEREFOR Original Filed July 31, 1941 3 Sheets-Sheet 2 Inventor-i George LRogers,

b'dj I Hi'sAttovneg Sept 8, 1942. a. 1.. ROGERS.

ELECTRIC SYSTEM AND INDICATING CIRCUIT THEREFOR Original Filed July 31/1941 3 Sheets-Sheet 3 Na h 51 g wall P v Inventor":

George L. Rogers,

atented Sept. 8, 1942 ELECTRIC SYSTEM AND INDICATING CIRCUIT THEREFOR George L. Rogers, Schenectady, N. Y., assignor to General Electric Company, a corporation of s NewYork J Original application July 31, 11941, Serial No.

Divided and this application March 1a, 1942, Serial No.434,944.

\ scams. (01.171-95) My invention relates to electric translating systems and more particularly to an indicating circuit therefor.

This application is a division of my copending patent application Serial No. 404,853, entitled Electric welding system, flied July 31, 1941, and which is assigned to the assignee of the present application. Certain broad features of the energy storage and dissipation system and the associated control apparatus are disclosed and,

claimed in the copending parent patent appli-' cationSerial No. 404,853.

In energy storage systems, such as capacitance energy storage systems wherein a capacitance is charged and discharged to eflect energization of a load circuit, it is frequently desirable to provide means for accurately indicating the state of energization of the capacitance. In accordance with the teachings of my invention, I provide a new and improved indicating circuit for systems of this nature.

It is a object of my invention to provide a new and improved indicating circuit.

It is another object of my invention to provide a new and improved electric valve indicating circuit.

It is a further object of my invention to provide a new and improved indicating circuit for electric translating apparatus of the energy storage type.

Briefly stated, in the illustrated embodiment of my invention I provide a new and improved indicating circuit for a, capacitor discharge type weldin system-wherein the magnitude of the direct voltage applied to the capacitance is accurately indicated. The indicating system is provided with a damping circuit comprising a capacitance and a resistance which are connected to a unidirectional conducting valve which is poled to transmit current in response to a voltage of a predetermined polarity of the first mentioned capacitance. The indicating device or instrument is connected across the damping circuit.

For a better understanding of my invention, reference may be had to the following description taken in connection with the accompanying drawings, and its scope will be pointed out in the appended claims; Figs. la, 1b and considered conJointly, diagrammatically illustrate an embodiment of my invention as applied to a welding machine which is energized from a poly phase alternating current supply circuit. Referring to the accompanying drawings and considering Figs. 1a, 1b and 10 arranged in a line from left to right in the order named, my invention is there diagrammatically illustrated as applied to an electric valve translating system for energizing a welding machine I. The welding machine I comprises welding electrodes 2 and 3, the latter of which may be operated upon by actuating means, such as a fluid operated piston, for controlling the pressure exerted. on the work by means of a conventional ram structure. The piston (not. shown) may be housed in a cylinder '4 to which an actuating fluid, such as air, is supplied by means of conduits 5 and exhausted therefrom by means of a conduit 5. The pressure exerted on the work may be controlled by means of a solenoid I which may control a valve mechanism (not shown).

The welding machine I includes a. transformer I provided with a magnetic core structure and having a primary winding 9 and a secondary winding it which is connected to the electrodes 2 and 3. The welding machine i is energized by transmitting thereto impulses of current and these impulses of current are, of course, transmitted to the welding electrodes 2 and 5. I employ suitable energy storage means, such as a capacitance I I, which is charged by means of a rectifier described hereinafter. In order to provide a flexible system wherein the magnitude of the capacitance is adjustable and, hence, to control the amount of power transmitted to the welding machine, I provide a plurality of capacitances I! which may be selectively connected in the system by means of a switch i3.

The capacitance H is charged from an alternating current supply circuit it through appara tus including a rectifying means I5 and a transformer I5. I provide a plurality of circuits condevice or an electric nected between the supply circuit l4 and the transformer l6 and having different impedances in order to charge the capacitance H at diflerent rates. For example, I may employ a plurality of charging circuits l1 and II, the latter of which has a substantially higher impedance than the former by virtue of resistances [9 which are connected in series with the'primary windings of transformer l6. Suitable circuit controlling means, such as switches 20 and 2|, provided with actuating coils 22 and \23, selectively connect the circuits I1 and I8 to the primary windings of transformer I6. Selective energization of actuating coils 22 and 23 may be obtained by means of a selector switch 24. A'manually operated switch 25 may be connected in series relation with circuits l1 and It to connect these circuits to the supply circuit ll.

The rectifying means 15 and associated control circuit may be of the type disclosed and claimed in a copending patent application Serial No. 398,807, of Orrin W. Livingston, filed June 19, 1941, and which is assigned to the assignee of the present application. This rectifying means may comprise a plurality of pairs of rectifiers arranged for full wave rectification. If desired, one rectitier of each pair, such as rectifiers 26, 21 and 28, may be of the uncontrolled type, and rectifiers 29, 30 and 3| may be of the controlled type each having a control member or a grid 32 the potential of which determines the amount of current conducted thereby and, hence, controls the rate at which the capacitance H is charged. I provide in series relation with the primary windings of transformer 16 reactors 33, 34 and 35 which limit the maximum current transmitted by rectifying means I 5 and hence limit the maximum rate at which the capacitanc I I may be charged. In this manner, the load imposed on the alternating current supply circuit I4 is also limited I provide excitation circuits 35, 31 and 38 for the rectifiers 29-3I, inclusive, which are of the type disclosed and claimed in the above-identified patent application and which control the conductivities of the rectifiers 23-31 throughout a region of substantially 240 electrical degrees of the voltage of the supply circuit I 4. The control of the conductivities of the rectiflers 29-3l is obtained by impressing on the grids 32 a resultant voltage composed of two components, one of which is a direct current biasing component the magnitude and polarity of which vary, and the other of which is a periodic voltage of substantially triangular wave form. The direct current or unidirectional component is varied by means of apparatus described hereinafter and controls the charging current transmitted to the capacitance ll. Each of the excitation circuits 35-33 includes means for producing a periodic voltage V the output circuit of of triangular wave form and includes transformers 39-41 which charge capacitances 42-44, respectively, through electric discharge paths furnished by apparatus described hereinafter. Each of the capacitances 42-44 is charged through a unidirectional conducting path which paths are provided by electric valves 45 and 46. The capacitances are discharged by means of circuits connected thereacross and which include resistances 41, 48 and 49. Points of the resistances are connected to the grids 32 of rectiflers 29-3l through current limiting resistances 50. Capacitances 5| may be connected between the cathodes and the grids 32 in order to absorb extraneous transient voltages. Excitation circuits 36-33, inclusive, are energized from the alternating current supply circuit 14 through a transformer 52 and a switch 53.

The electric valve 46 may be provided with two discharge paths, one of which may be employed as a rectifying path of a rectifier circuit which is energized by means of a transformer 55. Filtering capacitances 54 are connected across a voltage divider including a resistance 58. Transformer 55 may be energized from an intermediate circuit 51 which in turn is energized from the supply circuit 14 through transformer 56. Capacitance 59a is connected across one of the resistances 60 to limit the rate of rise of the voltage impressed on grids 32 of rectitlers 29-31, during the operation when the rectifying means I5 is rendered conducting, thereby preventing an excessive charging rate of the capacitance ll when the value thereof is relatively small. Capacitance 59b is connected between the common juncture of the resistances 60 and the cathode of the electric discharge device 61 and tends to bias the rectifiers 29-31 to cut-off before the circuit 55 operates if the rate of rise of the voltage of capacitance II is too rapid, thereby preventing overshooting of the capacitance voltage for small values of capacitive reactance. In this manner, the operation of the circuit is stabilized. Cathode heating transformers 6l-65, inclusive, may also be energized from circuit 51.

I provide a control circuit 66 for controlling the magnitude and polarity of the biasing potentir impressed on grids 32 of rectifiers 23-31 and thereby control the rate at which the capacitance l l is charged. The control circuit 33 includes an electric discharge device 61 which transmits variable amounts of current'through the resistance 68 and, hence, controls the magnitude of the voltage difference between the oathodes and grids 32 of the rectifiers 23-3l. Electric discharge device 61 may be provided with a control grid 69 and a screen grid 10. A suppressor grid may also be employed and may be connected to the cathode. Unidirectional current for energizing the anode-cathode circuit of electric discharge device 61 may be provided by a rectifier circuit including a transformer 1| and an electric valve 12 which charges a capacitance 13. A suitable filter circuit including inductance 14 and a capacitance 15 may be connected across the rectifier, and a predetermined component of the output voltage may be impressed on screen grid 10 through a voltage divider including resistances 16 and 11. The potential of the control grid 59 is controlled in response to the difference between. a positive reference voltage and a predetermined negative component of the voltage of capacitance II to vary the magnitude of the biasing potential imressed on grids 32 of rectiiieis 29-3l. The electric discharge device 61 is initially biased to cut-off during the early portion of the charging period of the capacitance H, and consequently permits the rectifiers 29-31 to conduct a greater amount of current during the early portion of the charging period. As the voltage of capacitance H rises; the electric discharge device 61 conducts increased amounts of current and consequently lowers the biasing potential from a positive value to a negative value and decreases the conductivity of the rectifiers 29-3l. This control may be obtained by means of the voltage divider comprising resistances 18, 19 and II which are connected across the capacitance II and which produce a predetermined negative component of voltage the magnitude of which varies in accordance with the voltage of the capacitance. Resistance 19 is provided with an adjustable contact 8| to provide a controllable component of voltage which is compared with the constant reference voltage, and which establishes the voltage to which capacitance II is charged. As a means for producing a constant positive reference voltage, I provide a rectifier including a transformer 82 which charges a capacitance 33 through one of the discharge paths of the electric valve 12. I connect a suitable constant voltage device, such as a glow discharge valve 34, in series relation with a resistance 85 across the capacitance 83, and the lower terminal of the glow discharge valve 84 is. connected to the lower terminal of resistance through resistances II and 81. The common juncture of resistances 34 and 8 is connected to control grid 63 through a current limiting resistance 99. The rectifier which energizes capacitance 93 also serves as a source 01' negative unidirectional biasing potential which may be impressed on the grids 32 through relay apparatus described hereinafter,

connected to charge a capacitance 9I through a resistance 92. The voltmeter 99 is connected across the latter two elements through a resistance 93. the capacitance II varies greatly during its-op.- eration, it has become important to provide some means for limiting the rate of change of the voltage appearing across the voltmeter and for providing some means for suppressing the magnitude of the negative voltage of the capacitance during the discharge interval. The rectifier 99 acting in conjunction with capacitance 9| produces a unidirectional component of voltage the magnitude of which is representative of the ma ,nitude of the positive capacitive voltage and suppresses the negative portion thereof.

I connectacross the capacitance II a discharge circuit including a resistance '94 and which includes the contacts of a relay 95. The relay 95 is provided with anactuating coil 96 and contacts 91 and 99, the former of which are connected in series relation with resistance 94. Contacts 99 are connected in series relation with a resistance 99 and when in a closed circuit position establish a discharge circuit across capacitance 9|.

I provide an undervoltage indicating and controlling circuit I99 which includes an electric discharge device IN. The voltage responsive circult I99 is responsive to the voltage of capacitance II and is connected to the terminals of capacitance II through a voltage divider including resistances I92I96, inclusive. Resistance I93 is provided with an adjustable contact I91 to control the magnitude of the voltage to which capacitance II is charged. The power for energizing the anode-cathode circuit of electric discharge device I9I is provided by means of a transformer I93. Electric discharge device I9l transmits energizing current to the actuating coil I99 of a relay 9 when the voltage of the capacitance II attains a predetermined value established by the setting of the adjustable contact I91. The potential of the cathode of discharge device I9! is established by means of a glow discharge valve III which is connected across a capacitance II2 through a resistance H3. The capacitance H2 is charged from the secondary winding of transformer I99 through an electric valve H4. The electric valve II4 may comprise a pair of electric discharge paths, one of which may be connected across the actuating coil I99 so that substantially constant unidirectional current is transmitted to coil I99. A cathode heating transformer H5 may be employed to energize the filaments of the electric valve II4.

Relay H9 is provided with contacts II6 which control the operation of a relay II1 having contacts III, Ill and I29 and an actuating coil I2I. when the voltage of capacitance II attains a predetermined value, relay H9 is operated effecting closure of contacts H3 01. relay H1 and ii In view of the fact that the voltage of contacts 1, 99 of relay I58 are closed, impresses on tacts I25. The actuating coil I24 is connected across circuit 51. The initiating circuit I22 also includes a start or charge switch I26 and a dlscharge switch I21 which are connected in circuit with actuating coil 96 of relay 95, and which also are connected in-circuit with an actuating coil I 29 of relay I29. The relay I29 is provided with a pair of sealing-in contacts I39 which areconnected around the charge switch I26. Relay I29 also includes a pair of contacts I3I which are connected in series relationwith the selector switch 24 so that either switching means 29 or 2i inay be energized, depending upon the setting of the selector switch 24.

As a means. for rendering the initiating circuit I22 inoperative in the event the voltage of capacitance II tendsto exceed a predetermined value, I provide an overvoltage protective circuit I32 which includes voltage responsive means, such as a spark'gap I33 and a relay I34 having contacts in series relation with switches I26 and I21. Circuit I32 also includes a resistance for dissipating the energy when the spark gap I33 breaks down.

I employ a pair of reversing contactors I35 and I36 connected to a winding section, such as the primary winding, of transformer 9 in order that successive impulses of current transmitted to transformer 3 flow in opposite directions. this manner, successive impulses of current tend to establish opposing magnetomotive forces and consequently prevent cumulative unidirectional magnetization of the core structure which would otherwise be present if the impulses of current were always transmitted in the same direction through the primary winding. Reversing contactor I35 is provided with power contacts I31 and I39 and con-trol contacts I39, and contactor I39 is provided with power contacts I49, HI and control contacts I42.

As a means for initiating the conduction of current through primary winding 9 of transformer 3 by the discharge of the capacitance ,1 provide an electric valve means I43 which is preferably of the type employing an ionizable medium, such as a gas or a vapor, and which may include a control member I44 of the immersionignitor type. The electric valve means I43 is rendered conducting by transmitting to control member I44 an impulse of unidirectional current and this may be effected by employing a control electric discharge device I45 which is connected to be responsive to-the-anode voltage of electric valve means I43. The discharge device I45 is provided with a control grid I46 and the discharge device I45 is maintained normally non-conducting by means of a negative unidirectional biasing potential which is impressed on the grid by means of a rectifier circuit including a transformer I41, a rectifier valve I49 and a capacitance I49.

To render electric valve means I43 conducting, the electric discharge device I45 is made to conduct current by impressing a relatively positive voltage on grid I46. This operation is performed by the energization of a transformer I59 which is energized byan impulse of current obtained by connecting its primary winding I I in circuit with a capacitance I52 which has previously been charged. Upon closure of contacts H9 of relay II1, capacitance I52 discharges through the primary winding of transformer I58 and produces a positive voltage which renders discharge device I45 conducting and consequently renders electric valve means I43 conducting.

In order to limit the magnitude of the reverse voltage of capacitance I I upon discharge, I connect across the primary winding 9 of transformer 8 an electric valve I53 which is also preferably 01 the type employing an ionizable medium. The electric valve I53 is rendered conducting by a control electric valve I54 which is connected to be responsive to the polarity of the anode voltage of electric valve I53. As soon as the voltage reverses sufliciently to cause appreciable current to flow through valve I54, electric valve I53 conducts current and thereby limits the magnitude I of the reverse voltage of capacitance I I.

I provide a starting circuit I55 which may include a manually operable switch I56 for effecting energization of a relay I51. Closure of the contacts of relay I51 energizes the actuating coil of the control relay I58. Control relay I58 is provided with an actuating coil I59 and contacts ISO-I64, inclusive. As an interlocking means between the means which exerts mechanical pressure on the work and starting circuit I 55, I provide pressure responsive means such as fluid pressure responsive switches I65 having contacts in series relation with the starting switch I56 and contacts I63 of relay I58. The power for energizing the actuating coil of relay I51 is provided by means of transformer I66 which may be energized from circuit 51. A precision switch MS may also be connected in the starting circuit I55 to provide an additional interlocking means so that the discharge of the capacitance II is not initiated until the movable electrode 3 and the associated ram are in predetermined positions. The switch MS may be connected to the ram structure by apparatus not shown.

I provide relays I61 and I68 for controlling the energization of the actuating coils for the reversing contacts I and I36. The energization of actuating coils for relays I61 and I68 is in turn controlled by relay I69, and auxiliary relays I10 and HI.

I provide a current responsive means, such as a relay I12, which is responsive to the capacitance discharge current which is transmitted through primary winding 9 of transformer 8, and which initiates a series of operations. The relay in is designed to open its normally closed contacts I13 and close its normally open contacts I14 almost instantaneously upon the initiation of the condenser discharge, and is also arranged to drop out when the discharge current decreases to a predetermined value. The relay I12 controls the operation of its auxiliary relays I15 and 516.

Relay I16 is provided with contacts I11-I80, inclusive, and relay I15 is provided with contacts i8I and I82. Relay I16 performs a number of operations upon energization, one of which is to operate a timing circuit, described hereinafter, through contacts I11, and another of which is to deenergize the actuating coil I2I of relay I I1 thereby removing the negative biasing potential "from the grids 32 of rectifiers 293I by virtue of the operation of contacts I80. Another function of the relay I16 is the deenergization of the actuating coil of relay I61 by means of contacts I19, and a still further function of the relay I16 is to control the energization of the actuating coil of relay I10. Relay I15 controls the energization of the actuating coil of relay I16.

I employ a plurality of timing circuits I 83, I34 and I which control the sequence of the steps in the welding operation. Circuit I83 may be arranged to operate instantaneously or with a time delay and controls the time at which current is transmitted to the work in response to the operation of the start switch I56. Circuit I84 controls the hold time that determines the time during which pressure is applied to the work, and circuit I85 controls the interval of time between successive applications of current and pressure to the work in the event it is desirable to transmit a number of impulses of current to the work. The system may be operated, without using circuit I85, by use of switch Circuits I83-I85, inclusive, are of the type disclosed and broadly claimed in U. S. Letters Patent No. 2,171,347, granted August 29, 1939, upon an application of E. D. Schneider and which is assigned to the assignee of the present application. The circuits I83-I85 are similar in construction and arrangement with the exception of the relays I81, I88 and I89 which are respectively connected in the circuits. Each of the circuits operates to effect energization of the associated relays a predetermined interval of time after the application of energizing voltage to the respective circuits.

Considering circuit I83 in particular, means are provided by way of switches I90 and Ill for adjusting the circuit to respond instantly, or to respond with a time lag, upon operation of switch I56. When switch I9I is closed and switch I90 is open, the circuit I83 operates instantaneously; vand when switch I90 is closed and switch |9I is open, the circuit operates with a time delay. Relay I 81 is provided with contacts I92, I93 and I94. Contacts I92 and I93 are connected to capacitance I52 and control circuit 66 through circuits I95. Contacts I93 serve to close the circuit for connecting the capacitance I52 to transformer I50 to efiect discharge of the capacitance through the transformer and to render electric valves I45 and I43 conducting. Contacts I92 are arranged to close the circuit for charging the capacitance I52 from the rectifier of the control circuit 66. Circuit I83, which is representative of circuits I83'-I85, includes an electric discharge device I96 which is normally biased to the nonconducting condition by impressing on grid I91 thereof a hold-ofi voltage by means of a capacitance I98 and a voltage divider including resistances I99. A predetermined interval of time after the application of voltage to circuit I83, the hold-oil voltage of capacitance I98 decreases suiliciently in magnitude to cause the electric discharge device I96 to conduct current, and consequently current is supplied to the actuating coil of relay I81, causing it to move to the energized position. Upon removal of the energizing voltage from circuit I83, relay I81 moves to its deenergized position.

Relay I88 of hold circuit 200203, inclusive. Contacts 200 and 20I serve to control the time-01f circuit I85, when employed, and contacts 202 are interlocking arrangements for controlling circuit I83. Contacts 203 control the energization of actuating coil I59 of relay I58.

A selector switch having contacts 204a and I84 includes contacts -ior operating the electrodes.

284i: as a means for operating the weldin; machine through its sequence without supplyin welding current to the work and for testing the operation of the welding machine and With switch 284 in the welding operating position, its contacts 28441 are closed and its contacts 28th are open. In the mechanical operating position, these contacts are open and closed respectively. Contacts 284a open the circuit to relay I88 or I81, preventing discharge oi! the capacitors through the welding transformer. Contacts 288b' allow completion oi! the actuating coil circuit of.re-' lay I15 when relay I81 of circuit I88 operates. *A further selector switch 285 serves as a means to bring the electrodes of the welding machine down on the work for positioning purposes, and then to proceed with the sequence operation or to raise the electrodes, as desired. with switch 285 arranged so that its contacts 285a and 285!) are closed, the sequence of operation proceeds in the normal manner. With switch 285 in the "apply electrode pressure only" position, these contacts are open and relay I58 cannot seal itself around relay I'I.

In order to permit the movement of the electrodes 2 and 3 away from the work rapidly after the transmission of the welding current to the 'work, I employ a contactor 288 having an actuating coil 281 and contacts 288 which when in the closed position short-circuit the secondary winding I8 of welding transformer 8. The contactor 205 is energized by means of contacts III of relay. I58 to open the short circuit path immediately preceding the welding operation, and to close the short-circuit path near the end of the impulse of current, thereby providing a path for the flow of current due to the inductance of the transformer, and permitting movement of the electrodes away from the work without causing appreciable sparking. A switch 208 may be employed to shunt the contacts 0! one o! the pressure switches I85 and switch MS.

The operation of the embodiment oi my invention diagrammatically illustrated in Figs. la, Ib and lo will be explained by considering the system when it is arranged to operate to supply a single impulse oi! current to the work inresponse to the operation of the starting switch I55. In order to obtain this control, switch I85 is moved to the open circuit position. When it is desired to effect the transmission oi! current to the work, as soon as the pressure is applied circuit I83 is arranged to. operate instantaneously and switch I9I is closed and switch I98 is open.

Selector switch 24 is moved to either the right or the left to selectively energize either switch 28 or switch 2i, which thereby controls the rate at which the capacitance II is charged from the supply circuit I4 through rectifying means I5. When switch is closed and 2I' is open, the capacitance is charged at a higher ratedue to the'lower impedance of this circuit. The maximum rate at which current .is transmitted to the capacitance II is, of course, limited by the reactors 83-45, inclusive, which are connected in series relation with thepower transformer I8 and the rectifying means I5. Switch 284 is placed in the welding operating position and switch '20: is placed in the normal operating position; that is, the contacts of these switches areclosed. The manually operable switches and 53 are then moved to the closed circuit position.

Closure of switch 58 supplies power to the cuit "thereby permitting the recti control circuits and cathode heating elements of the electric valves. Relay I8! is also enerthrough the normally closed contacts I18 01 relay I18 and the normally closed cont'acts of s relay I88, thereby eiiecting closure of its contacts in the actuating coil circuit oi'reversing contactor I88. At the end of a time delay interval, such as flve-minutetime delay period topermit the cathodes of the electric valves to attain safe operating temperatures-time delay relay I28 closes its contacts I25 in the initlatinl circuit I22. I

Operation may now be started by manually operatingthe charflini switch I25 in the initiating circuit I22. Closure of switch I28 energizes the auxiliary relay I28 which seals itseli inaround the charge switch I28, and one contact of which closes to effect energization of the actuating coil of either switch 20 or 2I, depending upon the one selected by the position of the selector'switch 24. Upon closure of the selected switch, the transformer I8 is energized from the supp y cirmeans I5 to start the charging operation of the capacitance II. At the same time, relay 85 is energized opening its contacts 81 and 88 thereby opening the discharge path around capacitance II and also opening the discharge path which is connected across the indicating circuit including voltmeter 88. As the capacitance II attains a predetermined voltage, preselected by the setting or contact 8I or resistance I8,'the control circuit 86 reduces the charging rate of capaci-' tance II to .that value'which is just sumcient to maintain the desired voltage. A detailed description of the operation of circuit 88 is given hereinafter. When the capacitor-voltage attains a predetermined value, the voltage responsive circuit I08 operates to eflect energization of coil is of the undervoltage relay m. Upon operation of relay IIII, its contacts H8 in the coil circuit or relay I I I are closed.

The weldingmachine I may now be started by the operator by closing the starting switch I55. Closure of switch in energizes. relay in eflecting closure of its normally open contacts. Operation of relay I5'I energizes the'actuating 0011 I58 of relay. I58 from circuit 51. The circuit through which coil I58 is energized includes the lower terminal of circuit 51, coil I58, contacts 288, contacts of relay I51 and the upper terminal of circuit 51.

Upon operation or the relay I58, closure of its contacts I84 eilects energizatlon of the operating solenoid 1 in the fluid system which admits the fluid to the operating mechanism of the weldin ram. This starts the movement of the ram down towards the work. A second contact I82 of relay I58 energizes the coil of contactor as through the contact of relay I81, previously mentioned, and a normally clomii interlock contact or contactor I35. Contactor I88 closes its power contacts I48 and Ill in the circuit between the capacitance II and the welding transformer 8, thereby preparing this circuit for the discharge of the capacitance II. A third set of contacts IN of relay I58--energizes 0011 281 01 relay 2Il5,v

opening the short circuit path across secondary winding I8 of welding transformer 8 to prepare it for operation. A fourth set of contacts I88 of relay I58 seals around'the contacts oi relay I51; and a fifth set of contacts I83 of relay I58" closes the circuit for eilecting application of voltage to timing circuit I88 to prepare it for operation.

As the contacts of relay I51 closed, the actuating coil of relay II 1 was energized and this relay sealed itself in around relay IIO, provided of course the voltage of capacitance II has been maintained at the selected value.

When relay II 1 closes its contacts. contacts II8 thereof apply negative bias voltage to grids 32 of rectifiers 29-3I, thereby preventing further charging operation of capacitance I I. Con

tacts II9 of relay II1 close in the circuit of primary winding I5I of transformer I50, thereby preparing the discharge circuit for subsequent completion by relay I81.

As the movable electrode 3 is moved downwardly by the ram, it places the electrodes on the work and applies pressure thereto. Upon the ram reaching the proper position, the switch MS is closed. .If the contacts of the pressure switches I55 are also closed, indicating the presence of suflicient fluid pressure, relay I81 of timing circuit I83 is energized without time delay and effects operation of its contacts. Contacts I 92 are opened, thereby opening the charging circuit for capacitance I52, and contacts I93 are closed completing the circuit for the discharge of the capacitance I 52 through the primary winding I755 of transformer I50, through contacts I I8 of relay II 1. Capacitance I52 upon discharge induces a positive impusle of voltage in the secondary of transformer I50.

Th'm impulse of voltage introduced in the secondary winding of transformer I50 is suflicient to overcome the negative bias voltage impressed on grid I45 of control electric valve I45 to cause this valve to conduct current and thereby transmit an impulse of energizing current to the control member I 44 of electric valv I13. As a result, the capacitance H is discharged through the primary winding 9 of transformer 8 through the following circuit: the circuit including the actuating coil of relay I12, contacts MI of contactor 236, the primary winding 9, contact I40 and the anode-cathode circuit Of electric valve I43. This discharge current develops in the welding transformer the voltage and current which produces a weld in the work being processed. As the discharge operation proceeds, if the load circuit is sufficiently inductive to tend to produce an oscillatory discharge the voltage across capacitance Ii tends to reverse, thereby raising the potential of the anode of electric valve I53 to cause the electric valve I53 to conduct current. Of course, since its control valve E55 is connected to th anode, the valve I54 conducts current, first efiecting the transmission of energizing current to the control member thereof and subsequently rendering valve I53 conducting. Under these conditions, the electric valve I53 conducts current and limits the inverse voltage of capacitance II to a low value established by the current maintaining voltage of the valve. The welding transformer 8 continues to dissipate energy due to the operation of electric valve As the discharge of capacitance II takes place, the current responsive relay I12 is energized opening its normally closed contacts I13 and closing its normally open contacts I14, effecting energization of the coil of auxiliary relay I15, which closes contact I ill in the actuating coil circuit of relay I16 and seals itself in around the contacts of relay I12 by means of contacts I82.

The capacitor discharge continues and as the charging current decreases near the end of the impulse the relay I12 drops out inasmuch as it is designed to move to the deenergized position when the discharge current decreases to a. predetermined value, Upon dropping out, relay I12 closes its contacts I13 and efiects energization of the actuating coil of relay I15.

Upon operation, relay I15 closes its normally open contacts I11 to apply energizing voltage to th hold timing circuit I88 and starts the hold time operation. Normallyclosed contacts I of relay I15 are open to deenergize the coil I2I of relay II1, thereby opening the contacts III of the latter relay and removing the hold-oil or; bias voltage from grids 32 of rectiflers 29 3I, thereby permitting a subsequent charging operation of capacitance II by rectifying means I8. A second normally closed contact I18 of relay I10 is open to deenergize relay I61 which in turn opens its contacts, effecting deenergization of the actuating coil for contactor I38. Contacts I40 and HI of contactor I35 thereby open th circuit for primary winding 8 at a relatively low value of current. A second normally open contact I18 of relay I18 closes the actuating coil circuit of auxiliary relay I10. One normally open contact of relay I10 closes to energize the coil of auxiliary relay I69 which seals itself in around the contact of relay I10 through a normally open contact. A normally open contact of relay I1! is also actuated, thereby opening the actuating coil circuit of relay I51 and closing that of relay I58.

At the completion of th timing interval established by circuit I84, relay I88 i moved to the energized position. A normally open contact 200 is closed to seal this timing circuit around one contact of relay I18, and th second normally open contact closes to energize the off-time relay I when switch I86 is in the closed or repeat position. Since it has been assumed that switch I85 is in the open circuit position or the nonrepeat position, the circuit I 85 is ineffective. A normally closed contact 203 of relay I88 opens the circuit for the actuating coil I58 of relay I58 which thereby moves to the deenergized position. By so operating, relay I58 performs the following operations: deenergizes the timing circuit I83 and relay I81; opens the sealing circuit around relay I51; opens the actuating coil of contactor I35 which was previously opened by opens the actuating coil circuit of relay 208 and opens the circuit for energizing th solenoid 1. Upon closure of contacts 208 of contactor 206, the secondary winding of transformer 8 is short-circuited, thereby permitting the electrode 3 to rise without involving sparking between electrodes 2 and 3. A second normally closed contact of relay I88 opens a circuit to deenergize relay I15 and I16. One normally closed contact of relay I16, that is, contact I80, closes in the coil circuit of relay II 1 to prepare the system for re-operation. A second normally closed contact I19 of relay I16 completes the coil circuit of relay I51 which claofises its contacts in the coil circuit of contactor Normally open contact I18 of relay I15 opens the circuit of relay I10 which drops out.

No further operation occurs so long as relay I51 is energized, since relay I88 is sealed in and its contacts prevent closure of relay I58 thereby preventing the reinitiation of the sequence. As soon as the operator releases the relay I51 by opening switch I58, relay I88 drops out releasingits sealed-in circuit, and upon reclosure of relay I51 by operating switch I58 the sequence again proceeds in the same manner as above stated with the exceptionjhat contactor I35 is now energized through the contacts of relay I88. Therefore, the capacitance II discharges through the primary winding! in the reverse direction due to the fact that power contacts I31 and I88 are closed and power contacts I80 and Ill are open. When relay I10 is energized, one of its normally open contacts completes a short circuit around the coil of relay I88 which now' drops out to restore the circuits of I81 and I88 to their original condition and removes the seal around the contact of relay I10. When relay I10 drops out upon the opening of relay I18, the coil of relay I1I is deenergized and relays I89I1I" are restored to their initial positions.

With switch I88 in the repeat position, upon energization of relay I81 the oil-time relay I85 starts to time and upon completion of its timing operation opens its normally closed contact in circuit with relay I88. Relay I88 is thereby deenergized and transfers its contacts to permit relay I58 to reclose and repeat the operations so long as relay I51 is maintained energized by the closure of the starting switch I 58. At any time that the relay I51 is open during the sequence of control, the operation will proceed until relay I58 is deenergized at which time operation will cease until relay I51 is reclosed.

It, when relay tance II is below tact II8 of relay IIO will not be closed and relay II1 will not operate. Should the voltage of capacitance I I attain the desired value before switch MS closes, however, relay I I1 will operate and the sequence will proceed normally. If, however, the capacitance does not attainthe desired value of voltage before MS closes, the open contacts of relay H1 in the circuit for primary winding I5I of transformer I50 prevents discharge initiation, and since relay I12 is not energized further operation of the equipment is prevented and manual means must be used to clear the machine. This manual means is effected by moving switch 205 to the apply electrode pressure only position and releasing relay I51 by operation of the switch I58. This permits-relay I58 to drop out without carrying through the usual sequence of operation. When using air or hydraulic operated welding machines in which no provision is made for initiating the discharge of capacitance I I by the position of the moving electrode or the position of the ram which operates the and 209 are closed and switch I8I is open. This arrangement effectively shunts the fluid initiating circuit and places circuit I83 in a condition to operate its contacts at definite adjustable times after relay I58 operates. The sequence of operations proceeds exactly as explained above with the exception that the discharge of capacitance II is initiated at a definite time after the pressure is exerted on the work, and that in the event the capacitance voltage is below the predetermined value when discharge is attempted the machine will pause with the electrodes in the welding position until the proper voltage is reached. When the proper voltage is'attained,

the welding operation will proceed in the normal manner.

I58 closes, the voltage of capa'ci-' the preselected value, the con-,

electrode, switches I90 selecting a rapid or slow charging rate for ca. pacitance II. Selector switch 208 provides a means for operating the welding machine through its sequence without welding when it is desired to test the machine for operation and for adjusting the electrodes by bringing the electrodes together in a hammer action. With switch 288 in the welding position, its contacts 2080. are closed and its contacts 20: are open. .In the mechanical operating position, these contacts are opened and closed respectively. Contacts 204a open the circuit to contactor I35 or I38, preventing discharge of capacitance I] through the welding transformer. Contacts 208!) allow completion of actuating coil circuit of relay I15 when circuit I88 operates. Since relay I15 is energized, it

.causes the relay I18 to operate exactly as though relay I12 had operated in the usual manner and the sequence of mechanical operation proceeds in the normal manner.

Selector switch 205 provides an arrangement for bringing the electrodes of the welding machine I down on the work for positioning purposes and for raising the electrodes as desired. The solenoid 1 may be energized and deenergized at will by operation of the starting switch I58 with the contacts of selector switch 205 in the open circuit position. Of course, since contacts 205bare open, discharge of the capacitance I I is prevented because the contacts of relay I81 are in a position to prevent the transmission of an energizing impulse of current to transformer I50.

If, during the positioning operation, the electrodes are properly applied to the work and it is desired to continue without removing the electrodes therefrom, switch 205 is moved to the normal operation position and the sequence proceeds transformer I8 and the resultant voltage which is impressed on grids 82 of rectiflers 288I. When circuit I8 is connected the charging rate is substantially lower than when circuit I1 is employed due to the fact that circuit I8 includes resistances I8. In addition, the maximum charging rate is limitedby means of the series connected reactorsj8-85.

The amount of current transmitted by the rectifying means I5 is determined in a measure by the resultant voltage impressed on grids 02. This resultant voltage includes two components, one of which is a variable biasing voltage and the other of which is a periodic voltage of triangular wave selector switch 24 serves as an. arrangement for form. The latter component of voltage is produced by excitation circuits 38-88 and the variable unidirectional component is produced by control circuit 88. The magnitude of the biasing voltage impressed on grids 32 varies from positive to negative throughout the charging period of the capacitance II. During the initial portion of the chargin period the biasing voltage is a relatively high positive value due to the fact that electric discharge device 81 is biased to cut-off. As the charging operation proceeds, discharge device 81 begins to conduct current through resistance 88 and varies the potential of grids 82 to cause the rectifiers 28-8I to conduct a smaller amount of current.

, This selective operation of the control circuit 96 in response to the magnitude of the capacitance voltage is obtained by comparing a predetermined component of voltage derived from the capacitance with a fixed reference voltage. Glow discharge valve 84 provides the constant reference voltage which is compared with a component of voltage obtained from resistance 19 which is connected in a voltage divider across the capacitance II. Resistances 86 and 81 provide an arrangement for the comparison of these two voltages and the difference thereof is impressed on grid 69 of discharge device 61. It will be noted that the potential applied to grid 69 varies from a high negative value with zero capacitance voltage to a positive value as the potential of the capacitance is raised.

When the capacitance is discharged, the discharge device 91 is biased to cut-off and practically all of the supply voltage provided by the rectifier circuit of circuit 66 appears across this discharge device, placing a high positive bias on control grids 32 of rectifiers 29-3I. When this condition prevails, the capacitance II is charged at a relatively high rate limited by reactors 33-35 and either circuit I? or I8. As the capacitance H is charged, the negative potential derived from the voltage divider connected across the capacitance rises, but since the voltage of circuit 65 is comparatively large, the grids 32 rectifiers 293I are maintained positive until the discharge device El comes into operation. At a point in the rise of potential of the capacitance, the voltage impressed on grid 59 reaches a sufficiently low negative value to permit this discharge device to conduct current. Upon further rise of capacitance voltage, this discharge device increases current and consequently decreases the positive voltage applied to grids 32 due to the drop in voltage in resistance 68. At some point along this line, the increased negative voltage derived from the capacitance and the decreased potential across discharge device 6? results in sutflcient negative voltage on grids 32' to bias rectifiers L l-3i to cut-off, thereby stop ping the charging operation. As the charge of capacitance II leaks off, a point is reached at which the negative bias on grids 32 is sufficiently reduced to permit the rectifiers -3I to again conduct and restore the voltage of the capac tance ii to the desired value. In this manner, the capacitance voltage is always maintained at a predetermined value to assure uniformity of the weld.

Adjustment of the capacitance voltage may be obtained by means of contact SE of resistance l9. With the contact 35 at the -lowermost position, the maximum capacitance voltage is required to bias the rectifiers 23I to cut-off and, conversely, with the contact 8i at the uppermost position the capacitance voltage is minimum.

Capacitances 59a, 59b and resistances 60 constitute an anti-hunting circuit to assure stable operation of the rectifier during the charging operation. The capacitance 59a in combination with resistances 66 serves to eliminate the hunting action by limiting the rate of rise of the bias potential as the contacts II8 of relay II! are opened to start the rectifier. In this manner accurate phase control of the resultant grid voltage of rectifiers 29-3l is obtained even during the first few cycles of the charging operation. Capacitor 59b is connected to prevent overshooting of the voltage to which capacitance I I is charged. That is, the capacitance 59b introduced a stabilizing efi'ect by decreasing the conductivities of the rectifiers 29-3I directly in proportion to the rate at which the voltage ofcapacitance II "rises, thereby preventing overshooting of the capacitanc'e voltage. N

In connection with the indicating circuit including voltmeter 89, it will be noted that the presence of the rectifier assures that the voltmeter 89 indicates only the positive or forward voltage of capacitance II, and the charging circuit including capacitance 9| and the resistance 92 tends to stabilize the voltage which is impressed across the terminals of the voltmeter 99. Furthermore, contacts 98 of relay close a dis charge path to the capacitance -9| to discharge the capacitance 9 and reset the indicating circuit,

Referring now to the circuit which transmits the energizing impulse of current to transformer I50, capacitance I52 is charged by utilizing a voltage derived from the right-hand portion of control circuit 66. It will be noted that the normally closed'contacts I92 of relay I81 close the charging circuit for capacitance I52 and that the capacitance I52 is charged from the circuit including capacitance 83 and glow discharge valve 84. Upon operation of relay Iil in circuit I83, the charging circuit for capacitance I52 is opened by means of normally closed contacts I92 and the discharge circuit is closed by means of contacts I93. Of course, in order to eiiect the discharge of capacitance I92, contacts II9 of relay II! must be closed. In other words, the negative or biasing voltage is impressed on grids 32 by closure of contacts IIB, thereby preventing the rectifying means II5 from operating during the discharge of capacitance II.

One of the important advantages of apparatus built in accordance with my invention is the arrangement by which the impulses of current are reversed in direction relative to the power or welding transformer, so that cumulative unidirectional magnetization is prevented in this manner effecting a substantial uniformity in the character of the welds produced by the currents. Furthermore, the connection of electric valve means I43 in series relation with reversing con tactors I35 and I36 relieves the duty imposed cn the reversing contactors by the initiation. of the condenser discharge which is obtained by controlling the conductivity of this electric valve means so that the reversing contactors are not required to initiate the heavy current due to the discharge of capacitance, II. Although the reversing contactors are required to interrupt a relatively low value of current near the end of each impulse, the magnitude of this current is not suihciently great to deleteriously affect the life of the contacts of these contactors.

While I have shown and described my invention as applied to a particular system of connections and as embodying various devices diagrammatically shown, it will be obvious to those skilled in the art that changes and modifications may be made without departing from my invention, and I, therefore, aim in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In combination, a capacitance subjected to variations in potential and reversals of polarity, an indicating circuit comprising an indicating instrument connected in series relation with a rectifier across said capacitance, a damping ciraccusacuit connected across said indicating instrument including in series relation a second capacitance and a resistance, and a discharge circuit for discharging said second capacitance.

2. In combination, a capacitance, means for charging said capacitance, means for discharging said capacitance, an indicating circuit comprising an indicating instrument, a rectifier in series relation with said instrument so that said instrument indicates only voltage of one polarity impressed across said capacitance, a damping circuit connected across said instrument including in series relation a resistance and a second capacitance, a discharge circuit for said second capacitance, and means for controlling said discharge circuit.

3. In combination, an alternating current supply circuit, a capacitance, an inductive discharge circuit for said capacitance, an indicating circuit including an indicating instrument connected in series relation with a rectifier across said capacitance, a damping circuit for said instrument including in series relation a resistance and a second capacitance, and a discharge circuit for discharging said second capacitance.

4. In combination, a capacitance, means for charging said capacitance, a load circuit, means for discharging said capacitance to effect energization of said load circuit, an indicating circuit comprising an indicating instrument connected in series relation with a rectifier across said capacitance, a damping circuit connected across said indicating instrument and including in series relation a second capacitance and a resistance, and means for discharging said second capacitance.

5. In combination, a capacitance, means for charging said capacitance, an oscillatory discharge circuit for said capacitance, means for initiating discharge of said capacitance, and an indicating circuit comprising an.indicating instrument connected in series relation with a rectifier across said capacitance and a damping circuit connected across said 6. In combination, a capacitance, means for charging said capacitance, a load circuit, an oscilindicating instrument.

latory circuit connected between said capacitance and said load circuit and comprising means for discharging said capacitance therethrough, and an indicating circuit selectively responsive to the voltage of said capacitance incident to the charge of said capacitance established by said means and comprising an indicating instrument connected in series relation with a rectifier across said capacitance.

'1. In combination, a supply circuit, a capacitance, means for charging said capacitance from said supply circuit, a load circuit, a discharge circuit for said capacitance connected between said capacitance and said load circuit and comprising an appreciable inductance which with said capacitance tends to produce an oscillatory discharge, an indicating circuit selectively responsive to the voltage of said capacitance incident to the charging operation and comprising an indicating instrument connected in series relation with a rectifier across said capacitance, a damping circuit connected across said indicating instrument including in series relation a second capacitance and a resistance, and a discharge circuit for discharging said second capacitance.

8. In combination, a supply circuit, a capacitance, means for charging said capacitance from said supply circuit, a load circuit, means connected between said capacitance and said load circuit and comprising appreciable inductance thereby tending to make the discharge circuit for said capacitance oscillatory, means for initiating discharge or said capacitance, an indicating circuit selectively responsive to the voltage of said capacitance incident to the charging operation and comprising an indicating instrument connected in series relation with a rectifier across said capacitance, a discharge circuit connected across said indicating instrument including in series relation a second capacitance and a resistance, a discharge circuit for said second capacitance, and means responsive to said initiating means for controlling said discharge circuit.

\ GEORGE L. ROGERS. 

